XML is rapidly becoming the vehicle of choice as a definition language for the description of content-related structures. XML provides great flexibility and universality because XML provides a grammar that can express nearly any content. On the Internet in particular, the standardized representation of content structures fosters the development of previously unrecognized applications.
More and more, mission-critical applications are designed to run on the Internet. Adding the logical structuring capability of XML to the mix, and a new infrastructure that is ideal for running electronic business applications on the Internet becomes much more feasible. Databases can now be accessed directly via XML without having to use CGI and HTML or Java in addition. XML is generally a hierarchical structured data representation.
In addition to the rise of structured content like XML, relational databases have long been the bulwark of the information infrastructure of countless businesses. Relational databases provide a primary tool for business to maintain, access, and analyze data. Such database technologies have evolved over many years so that they are optimized for accessing and manipulating large information bases. Many businesses store the majority of their critical information in relational databases. Moreover, many Internet sites managed their data using relational database technology. This approach also makes it possible to develop database search engines for sifting through the large volumes of information that “live” on the Internet. Unlike XML, relational databases are not hierarchically structured but rather are relationally structured to provide efficient management of large amounts of data.
The combination of database technology with self-describing structure of hierarchical languages such as XML opens an interesting perspective for new applications. However, the melding of the kind of tree structures supported by hierarchical languages such as XML with the form of a relational data model presents a number of issues, some of which have already been addressed and solved. One vexing issue is presented when ensuring that seemingly inapposite theoretical constructs between the two data representations must be harmonized. Hence, a mechanism that facilitates the mapping between data in the form of hierarchical data structures and relational data structures is desirable.